Although I have never played this game personally, it sorta reminds me of Cube. Looks kinda fun and I would download it if my computer was strong enough (especially since I actually have experience in online FPS via Skulltag.) Well at least the original free version is still available.

Well, I just grabbed Version 0.6 of Xonotic off of Desura, and the game is certainly a lot better than Nexuiz was. Everything is, of course, a lot more graphically impressive than the state Nexuiz was left in and the game feels a lot more tight. Verson 0.6 feels more like a incremental update over 0.5, but it still plays a little better than the last one did. So things are actually looking up.